Sewage Treatment Plant No. 2 - Executive Summary

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Release prevention and emergency response policies 
Personnel at this City of Wichita (City) facility take a very active approach in maintaining and improving chemical safety.  This facility complies with industry-standard requirements for sewage treatment plants that use chlorine and sulfur dioxide in ton containers.  The policy at this facility is to adhere to all applicable federal, state, and local laws.  If an emergency were to occur, the policy is to notify the City Fire Department and request that they respond to the emergency. 
 
Facility and regulated substance    
This facility is a 54-million-gallon per day (average design flow) sewage treatment plant located in Wichita, Kansas.  The facility employs preliminary, primary, secondary, and advanced waste treatment processes.  The covered processes include the use of chlorine and sulfur dioxide chemicals.  Chlorine is used for disinfection to destroy pathogenic microorganisms in the plant effluent.  Sulfur dioxide is used for dechlo 
rination to reduce the toxic effects of chlorine in the receiving stream.  There are two chlorine contact channels, a dechlorination system, and reaeration chamber. 
 
Final clarifier effluent flows to the chlorine contact chamber where it is mixed with chlorine gas from the chlorination system.  The channels provide the necessary detention time for the chlorine to provide a thorough bacteria kill in the effluent.  At the end of the channels sulfur dioxide gas is added to the effluent to provide dechlorination.  Additional aeration is provided in the reaeration chamber prior to final discharge. 
 
The chlorine is provided through truck-delivered ton containers and the maximum intended inventory is 24,000 pounds.  The sulfur dioxide is provided through truck-delivered ton containers and the maximum intended inventory is 18,000 pounds.  The ton containers of both chemicals are stored in the disinfection building at the plant. 
 
Worst-case and alternative release scenarios 
The worst-case relea 
se scenario for chlorine involves the largest chlorine-containing vessel in the system, a one-ton container.  It can contain up to 2,000 pounds of chlorine.  The worst-case release analysis assumes all of these contents are released in 10 minutes.  The ton containers are partially enclosed at the disinfection building.  No passive mitigation was considered in the analysis for chlorine.  The distance to endpoint is 3.0 miles. 
 
The worst-case release scenario for sulfur dioxide involves the largest sulfur dioxide-containing vessel in the system, a one-ton container.  It can contain up to 2,000 pounds of chlorine.  The worst-case release analysis assumes all of these contents are released in 10 minutes.  The ton containers are partially enclosed at the disinfection building.  No passive mitigation was considered in the analysis for sulfur dioxide.  The distance to endpoint is 3.1 miles. 
 
 
The alternative release scenario for chlorine was based on a methodical analysis of accident history, 
process hazard analysis, experience at other similar company facilities, and industry experience.  The choice for alternative release for chlorine was the disconnection of the flexible tubing between the container and the header, resulting in a release of liquid chlorine.  Because it was assumed that the sensors and alarms would work, the duration of the release was assumed to be fifteen minutes before the leak would be shut off.  The distance to endpoint is 0.4 mile. 
 
The alternative release scenario for sulfur dioxide was based on a methodical analysis of accident history, process hazard analysis, experience at other similar company facilities, and industry experience.  The choice for alternative release for sulfur dioxide was the disconnection of the flexible tubing between the container and the header, resulting in a release of liquid sulfur dioxide.  Because it was assumed that the sensors and alarms would work, the duration of the release was assumed to be fifteen minutes befor 
e the leak would be shut off.  The distance to endpoint is 0.4 mile. 
 
For both analyses, the EPA's Risk Management Program Guidance for Wastewater Treatment Plants was used.  The results were verified using RMP*Comp, which is based on the formulae in the guidance document.  
 
Accidental release prevention program 
The facility's prevention program for both the chlorine and sulfur dioxide processes complies with the corresponding sections of EPA's 40 CFR part 68 accident prevention program rule for program level 2 processes and applicable state and local codes and regulations.  The chlorine and sulfur dioxide systems are design, installed, and maintained in accordance with state and local laws.  To achieve and maintain this compliance, the City has in place many procedural and technological safeguards.  The procedural safeguards include an employee training program and operating and maintenance procedures for those employees involved in operating the covered process.  The technological sa 
feguards include controls, sensors, alarms, relief valves, and industry standard systems.  All of these serve to prevent unintended releases of chlorine and sulfur dioxide, or at least minimize the effects of a release. 
 
Five-year accident history 
This facility has had two incidents of an unintended release of chlorine in the last five years.  The first was in February 1996 and occurred during the changing of in-line chlorine filters.  The amount released was calculated at 5 pounds.  The second incident was in June 1997 and occurred while an employee was changing chlorine containers and loosened a flexible connector while it contained chlorine gas.  This release was calculated to be less than 10 pounds.  In both cases, the employee was taken to the hospital, treated, and released.  These accidental releases resulted only in medical treatment and did not result in serious injury or property damage onsite or offsite. 
 
Emergency response program   
The facility has a written emergency resp 
onse and preparedness plan that is coordinated with local emergency responders.  The City of Wichita Fire Department is the primary responder.  City employees handle incidental releases of chlorine and sulfur dioxide and are trained and equipped to do so. 
 
The emergency response and preparedness plan includes causes and effects of emergencies, reducing system vulnerability and emergency planning activities.  The plan discusses mutual aid agreements with both the police and fire departments.   
 
Planned changes to improve safety 
The maintenance and improvement of safety is an ongoing job at this facility.  Safety training takes place throughout the year.  Safety-related recommendations from employees, whether made during formal sessions like hazard reviews or upon observation of a potential hazard, are always considered carefully for implementation.  This process is continuous and, even at times when no major process changes are anticipated, existing safety systems and procedures are fin 
e-tuned as a matter of course.   Currently, the recommendations made during the recent hazard review of both processes are under consideration.
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